Stent for improved transluminal deployment

ABSTRACT

A stent and method for manufacturing a stent comprising an expandable, generally tubular body portion in which one or both ends of the stent are provided with a generally rounded, smooth radiused portion that forms a bulbous protrusion out of the plane of the circumference of the stent. The design of the stent increases the profile of the end of the stent and decreases the risk of injury or vessel dissection during stent deployment.

FIELD OF THE INVENTION

This invention relates to medical implant devices. More specifically,the invention relates to an improved implantable stent apparatus for thetreatment of stenoses in coronary or peripheral vessels in humans.

BACKGROUND OF THE INVENTION

Cardiovascular disease, including atherosclerosis, is the leading causeof death in the United States. The medical community has developed anumber of methods and devices for treating coronary heart disease, someof which are specifically designed to treat the complications resultingfrom atherosclerosis and other forms of coronary artery narrowing.

An important development for treating atherosclerosis and other forms ofcoronary narrowing is percutaneous transluminal coronary angioplasty,hereinafter referred to as "angioplasty" or "PTCA". The objective inangioplasty is to enlarge the lumen of the affected coronary artery byradial hydraulic expansion. The procedure is accomplished by inflating aballoon within the narrowed lumen of the coronary artery. Radialexpansion of the coronary artery occurs in several different dimensions,and is related to the nature of the plaque. Soft, fatty plaque depositsare flattened by the balloon, while hardened deposits are cracked andsplit to enlarge the lumen. The wall of the artery itself is alsostretched when the balloon is inflated.

Unfortunately, while the affected artery can be enlarged, in someinstances the vessel restenoses chronically, or closes down acutely,negating the positive effect of the angioplasty procedure. In the past,such restenosis has frequently necessitated repeat PTCA or open heartsurgery. While such restenosis does not occur in the majority of cases,it occurs frequently enough that such complications comprise asignificant percentage of the overall failures of the PTCA procedure,for example, twenty-five to thirty-five percent of such failures.

To lessen the risk of restenosis, various devices have been proposed formechanically keeping the affected vessel open after completion of theangioplasty procedure. Such endoprostheses (generally referred to as"stents"), are typically inserted into the vessel, positioned across thelesion or stenosis, and then expanded to keep the passageway clear. Thestent overcomes the natural tendency of the vessel walls of somepatients to restenose, thus maintaining the patency of the vessel.

Various types of stents are currently under development, although todate none has proven completely satisfactory during testing. U.S. Pat.No. 4,655,771 to Wallsten describes a stent comprising a tube ofstainless wire braid. During insertion, the tube is positioned along adelivery device, such as a catheter, in extended form, making the tubediameter as small as possible. When the stent is positioned across thelesion, it is expanded, causing the length of the tube to contract andthe diameter to expand. Depending on the materials used in constructionof the stent, the tube maintains the new shape either through mechanicalforce or otherwise.

U.S. Pat. No. 4,733,665 to Palmaz describes a stent comprising a slottedstainless steel cylinder that forms a mesh when expanded. The stent isdelivered to an affected area by a balloon catheter, and is thenexpanded to the proper size by inflating the balloon.

Stents are typically delivered to affected areas of vessels usingstandard catheterization techniques. A thin walled hollow guidingcatheter is introduced into the body via a relatively large vessel, suchas the femoral artery in the groin area or the brachial artery in thearm by insertion through a hollow sheath. The guiding catheter ismaneuvered through an approximately 180 degree turn through the aorticarch to descend into the aortic cusp where entry may be gained to eitherthe left or the right coronary artery, as desired.

A flexible guidewire is inserted into the guiding catheter and advancedto the area to be treated. The guidewire is advanced across the lesionin preparation for the advancement of a catheter across the guide wire.Typically a balloon catheter carrying the stent is then introduced overthe guidewire to the area to be treated. Radiopaque markers in theballoon segment of the catheter facilitate positioning across thelesion. The balloon catheter is then inflated with contrast material topermit fluoroscopic viewing during treatment. The balloon is inflateduntil the lumen of the artery is satisfactorily enlarged and the stentis in place.

During delivery of the stent, the stent and balloon catheter mustnavigate narrow tortuous vessels into the site of a stenosis. Typically,the balloon and stent are covered with a sheath during delivery. Suchsheaths facilitate delivery of stents because the sheath prevents thestent from being dislodged from the delivery device. However, sheathsincrease the cross-sectional profile of the stent, necessitating use ofa guiding catheter with a larger internal diameter. The large diameterof the guiding catheter may increase the risk of complications at thepatient access site. Moreover, the larger cross-sectional profile of thestent delivery system may decrease the ability to deliver contrastmaterial through the guiding catheter to enable precise positioning.More important, an increased cross-sectional profile may make itimpossible to deliver a stent through narrow and tortuous vessels to thearea desired to be treated.

Stent delivery systems without sheaths have been proposed. For example,the Boneau stent described in U.S. Pat. No. 5,292,531 has been used witha modified delivery device described in co-pending U.S. patentapplication No. 08/451,270 which is hereby incorporated by reference.The disclosed delivery system secures the stent on the outside of theballoon without the need for a sheath.

However, attempts to deliver expandable stents without using a deliverysheath have resulted in a number of problems. First the relatively rigidstent may be dislodged from the more pliable balloon material of theflexible delivery device when contact occurs between the vessel wall andthe stent, particularly during passage through a curve. Additionally,the low mass of the rigid stents, and construction methods of somestents, causes the end portions to have small cross-sections and to besomewhat ridged and sharp. The small, sharp, cross-sections at the endsof the stents increase the risk that a stent will penetrate the vesselwall, particularly when the narrow, rigid end of a stent encounters acurve in a vessel. The flexible delivery device and balloon materialfollow the contours of the vessel, and when negotiating a curve, thedistal end of the more rigid stent may separate slightly from theballoon and delivery device. The separated, sharp distal end may causeabrasion or penetrate the soft tissues of the vessel wall.

These and other complications have resulted in a low level of acceptancefor such stents within the medical community for certain procedures, andto date stents have not been accepted as a practical method for treatingmany chronic restenosis conditions.

It would therefore be desirable to provide methods and apparatus, usefulfor treating chronic restenosis conditions, that enable delivery of astent without a sheath and which reduce the risk of vessel abrasion anddissection during delivery.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of this invention to providemethods and apparatus, useful for treating chronic restenosisconditions, that enable delivery of a stent without a sheath and whichreduce the risk of vessel abrasion and dissection during delivery.

A stent constructed in accordance with this invention may be in the formof an expandable, generally tubular body portion having two ends,wherein at least one end of the stent is provided with a generallyrounded, smooth radius.

The deployment methods for implanting a stent constructed in accordancewith the present invention include balloon expansion, self-expansion,self-retraction and mechanical expansion. Some of the intended usesinclude PTCA type stenting, PTA type stenting, graft support, graftdelivery, INR use, GI tract use, drug delivery, and biliary stenting.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an elevational sectional view of an illustrative prior artstent attempting to negotiate a curve in a narrow vessel.

FIG. 2 is an elevational sectional view of an illustrative stentaccording to the present invention attempting to negotiate a curve in anarrow vessel.

FIGS. 3A-3B show respectively, perspective and end views of anillustrative prior art mesh stent.

FIGS. 4A-4B show respectively, perspective and end views of anillustrative mesh stent constructed in accordance with the presentinvention and having bulbous portions created by bending the material ofthe stent wall at the apices of the stent outward.

FIGS. 5A-5B show respectively, perspective and end views of anillustrative mesh stent constructed in accordance with the presentinvention and having bulbous portions created by providing extramaterial at the apices of the stent.

FIGS. 6 shows a perspective view of an illustrative mesh stentconstructed in accordance with the present invention and having a radiusformed at the apices of the stent in the plane of the wall of the stent.

FIGS. 7A-7C show respectively, a prior art expandable wire-type stent,and two alternative embodiments of a stent similar to the stent of FIG.7A but which additionally incorporate features of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

In overview, an endoprosthesis constructed in accordance with thepresent invention comprises an expandable, generally tubular bodyportion having two ends. In accordance with the present invention, atleast one end of the stent is provided with a generally rounded, smoothradiused portion that forms a bulbous protrusion out of the plane of thecircumference of the stent. The methods and apparatus of the presentinvention are illustratively described with respect to the low-mass,unitary mesh-like stent structure described in U.S. Pat. No. 4,733,665.It will of course be understood that the present invention is notlimited to that stent structure, but is generally applicable topreviously known stents such as those described above to reduce thepotential for vessel abrasion and dissection during delivery.

FIG. 1 is a diagrammatic side view of prior art stent 11 showncompressed on a delivery device, in this case on balloon 12 of ballooncatheter 13. Stent 11 is shown attempting to negotiate a curve whilepassing through the lumen of narrow vessel 14. Distal end 15 ofsubstantially rigid stent 11 separates from the pliable balloon materialand flexible catheter 13 as catheter 13 and balloon 12 curve to followthe contour of the vessel 14. The separation is illustratively shown asgap 16. Distal end 15 contacts intima 17 of vessel 14 becausesubstantially rigid metallic stent 11 does not bend around the curve inthe vessel wall as readily as flexible catheter 13 and pliable balloon12. Depending upon the condition of vessel 14, contact by distal end 15of stent 11 may cause abrasion to intima 17, or even dissection ofvessel 14. More important, it may be impossible to deliver stent 11 tothe desired location in vessel 14 if stent 11 cannot be maneuveredthrough the turn.

FIGS. 3A-3B show views of a typical mesh stent 31 such as described inPalmaz U.S. Pat. No. 4,733,665. FIG. 3A is a perspective view of theentire stent while FIG. 3B shows an end view of the stent. In FIG. 3Athe apices 32 of the stent are shown having right-angled corners 33. Itis believed that the sharpness of these corners in combination with thethin profile of the flat end of the apices 32 contribute to the poortrackability of this stent when used without a sheath. In FIG. 3B thesmall profile presented by the apices 32 of the stent 31 to the vesselwall is readily observed. The thickness of the stent material in suchstents is typically less than 0.005 inches.

Referring now to FIG. 2 which is illustrative of a stent 21 embodyingthe principles of the present invention as described. Items common withFIG. 1 are numbered identically with those of FIG. 1. Distal end 22 andproximal end 23 of stent 21 are provided with a radiused or bulbousportion 20 that protrudes beyond the outer circumference of the stent toincrease the surface area of ends 22, 23. Bulbous portion 20 eliminatesany sharp edges in the formation of stent 21 which may be formed of thinmaterial. As stent 21 negotiates a curve, the curved surface reduces therisk that the ends of stent 21 will penetrate vessel 14.

Referring now to FIGS. 4A-4B, 5A-5B, radiused portions formed by severalmethods are shown. It is apparent from these figures that the apex ofthe stents of the present invention presents a larger radius profile tothe wall of the vessel than does the apex of the prior art device shownin FIGS. 3A and 3B.

Stent 41 of FIGS. 4A-4B is formed by bending outward the stent materialin the region of apex 42 of the stent. As shown in FIG. 4B the bendingof the stent material adds radius 43 to the apex 42 of stent 41. Asshown in FIG. 4B the bending of the stent material increases the profileof apex 42 that is presented to the wall of the vessel, thus reducingrisk of injury or dissection.

Stent 51 of FIGS. 5A-5B is formed by adding material 54 in the region ofapex 52 of the stent. As shown in FIG. 5B the additional material addsradius 53 to the apex 52 of stent 51. As shown in FIG. 5B the additionalmaterial increases the profile of apex 52 that is presented to the wallof the vessel, thus reducing risk of injury or dissection.

The material 54 added in the region of the apex may have the samecomposition as the material of the stent or alternatively may have adifferent composition. For example the added material may be a metal ora non-metal. Metal material may be added to the radius in molten orpowdered form and solidified around the apex using conventionalmetallurgical and soldering techniques. In addition, the radiused orbulbous portion may then be polished if desired to eliminate anyirregularities.

A polymer material may also be formed around the apex of the stent inpowdered or molten form. Alternatively, heat-shrink plastic elements maybe inserted over portions of the stent and heat treated at the apexlocations. Where a polymer is chosen to create the radiused portion, asuitable biocompatible polymer may be chosen which forms a good bondwith the vessel over time. This integration of the ends of the stentwith the intima of the vessel wall is expected to have the additionalbenefit of anchoring the stent over time.

The additional material at the apex of stent 51 in the region of apex 52may also be provided by thickening the stent. For example, the apex of astent such as stent 31 of FIG. 3A may be heated to form a bead ofsoftened or molten stent material which forms the radius when cooled as,illustrated by stent 51 of FIG. 5A. The radius 53 may then be polishedif desired to eliminate any irregularities. The thicker stent materialadds radius 53 to apex 52 of stent 51. This additional thickness of thematerial increases the profile of apex 52 of stent 51 that is presentedto the wall of the vessel as described hereinabove. It will berecognized by those skilled in the art that the increased thickness ofmaterial forming the radius at an apex of stent 51 also may be providedby using powder metallurgy techniques or selective machining.

Stent 61 of FIG. 6 illustrates an alternative embodiment of the presentinvention in which the apex of the stent is provided with a radius inthe plane of the wall of the stent. The apices 62 of stent 61 arerounded off at the edges 63. It is believed that while not necessarilyincreasing the thickness of stent 61 in the region of apices 62 of thestent, the radius provided by rounding the apices of the stent willimprove trackability of the stent. The profile of the stent mayadditionally be increased by forming another radius on the stent byadding material in the region of the apices 62 as shown in FIGS. 5A and5B.

The stent of FIGS. 7A-7C is illustratively formed from a wire structurefor example, like the stent described in Boneau U.S. Pat. No. 5,292,331.Such wire-type stents can be manufactured either by bonding togetherseparate elements into the desired configuration or by bending a unitarypiece of wire-like material. According to the present invention, aradiused portion can be provided on such stents by adding material orthickening the wire-like material at the apices of the stent asdescribed above with respect to FIGS. 5A-5B. Referring to FIG. 7B theadditional material 73 adds a radius 74 to stent 72 that increases theprofile of apex 72 of stent 71. Stent 71 of FIG. 7C is formed byproviding a twist 75 in the wire in the region of apex 72 of the stentto form radiused portion 76. The bending of the apex adds radius 76 tothe stent 71. The radius increases the profile of apex 72 of stent 71,as described hereinabove.

The present invention provides further advantages during deployment, asdescribed hereinabove. The stent and radii are preferably formed fromradiopaque materials. Since there typically is more material in the endregions of the stents of the present invention compared to the stents ofthe prior art, the increased amount of radiopaque material at the endsof the stent are more clearly outlined during deployment, therebyassisting accurate placement of the stent.

While one application for the above-described stent includes treatmentof cardiovascular disease such as atherosclerosis or other forms ofcoronary narrowing, the present invention may also be used for treatmentof narrowed vessels in other components of the vascular system, forexample, the kidney, leg, carotid artery, or elsewhere in the body. Aswill of course be appreciated, the size of the stent, as well as itsexternal characteristics, may need to be adjusted to compensate for thediffering sizes of the vessel to be treated.

While this invention has been described in connection with anillustrative preferred embodiment thereof, modifications and changes maybe made thereto by those skilled in the art without departing from thespirit and scope of the invention. Accordingly, the scope of thisinvention is to be limited only by the appended claims.

What is claimed is:
 1. In a stent having first and second ends and awall surface disposed between the first and second ends and having afirst diameter that permits intraluminal delivery and a second expandeddiameter wherein the stent supports a lumen of a body passageway, theimprovement comprising:a radiused or bulbous region disposed on thefirst end of the stent in a plane transverse to the stent;the radiusedor bulbous portion increasing the profile of the stent in the region ofthe first end, to reduce the risk of injury to the lumen of the bodypassageway during introduction of the stent.
 2. The stent as defined inclaim 1 wherein the second end is provided with a radiused or bulbousportion.
 3. The stent as defined in claim 1 wherein the radiused orbulbous portion is formed by adding material to the first end out of theplane of a circumference of the stent.
 4. The stent as defined in claim3 wherein the material has a different composition than the stent. 5.The stent as defined in claim 1 wherein the radiused or bulbous portionis formed by thickening the first end of the stent.
 6. The stent asdefined in claim 5 wherein the radiused or bulbous portion is formed bya step of heating the first end of the stent.
 7. The stent as defined inclaim 6 wherein the step of heating the first end of the stent isaccomplished using a laser.
 8. The stent as defined in claim 1 whereinthe radiused or bulbous portion is formed by bending the wall of thestent at the first end.
 9. In a stent for implantation within a lumen ofa vessel within the human body comprising a plurality of N substantiallystraight segments of wire-like material, each segment having first andsecond ends, the first end of the first segment being connected to thefirst end of the second segment at a first apex, the second end of thesecond segment being connected to the second end of the third segment ata second apex, and so on until the second end of the Nth segment isconnected to the second end of the first segment at the Nth apex, theimprovement comprising:a radiused or bulbous portion disposed on eachodd-numbered apex and increasing the profile of the apex to reduce therisk of injury to the lumen of the body passageway during introductionof the stent.
 10. The stent as defined in claim 9 wherein eacheven-numbered apex is provided with a radiused or bulbous portion. 11.The stent as defined in claim 9 wherein the radiused or bulbous portionis formed by adding material to each odd-numbered apex out of the planeof a circumference of the stent.
 12. The stent as defined in claim 11wherein the material has a different composition than the stent.
 13. Thestent as defined in claim 9 wherein the radiused or bulbous portion isformed by thickening of the apex of the stent.
 14. The stent as definedin claim 13 wherein the radiused or bulbous portion is formed by a stepof heating the apex of the stent.
 15. The stent as defined in claim 14wherein the step of heating the stent is accomplished using a laser. 16.The stent as defined in claim 15 wherein the radiused or bulbous portionis formed by bending the odd numbered apices of the stent.
 17. A methodof manufacturing a stent comprising the steps of:providing a tubularmember having two ends and a plurality of apices at each end; increasingthe profile of a plurality of the apices so as to reduce the risk ofinjury to the lumen of the body passageway during introduction of thestent.
 18. The method as defined in claim 17 wherein the step ofincreasing the profile of a plurality of the apices comprises the stepof adding material to the apex out of the plane of a circumference ofthe stent.
 19. The method as defined in claim 18 wherein the step ofincreasing the profile of a plurality of the apices comprises the stepof adding a polymer material to the apex out of the plane of acircumference of the stent.
 20. The method as defined in claim 17wherein the step of increasing the profile of a plurality of the apicescomprises the step of thickening an apex of the stent.
 21. The method asdefined in claim 20 wherein the step of thickening an apex of the stentcomprises the step of heating an apex of the stent.
 22. The method asdefined in claim 21 wherein the step of heating an apex of the stentcomprises the step of directing a laser at the apex of the stent. 23.The method as defined in claim 17 wherein the step of increasing theprofile of a plurality of the apices comprises the step of twisting theapex of the stent out of the plane of a circumference of the stent.